It may seem ironic, but the same physical law that governs the decay process also makes engines work and physical life possible. The second law of thermodynamics, also known as the law of increasing entropy or simply the law of increasing decay, fundamentally has to do with heat transfer from hot bodies to cold.
The rate at which decay proceeds in the universe is extremely high. That may seem bad, but it’s not. If the rate of decay were any lower, galactic systems would trap radiation in such a manner that stars could not form. Starless galaxies would fill the universe. On the other hand, if the decay rate were slightly higher, no galactic systems would form at all. In either case there would be no “terrestrial ball” to serve as a home for life.
The extreme predominance of decay, or heat dissipation, not only makes Earth possible but also makes Earth a suitable home for physical life in countless ways. It impacts climatic conditions, chemical reactions, and plate tectonics, for example. What’s more, this level of heat flow makes possible all forms of work, including such basic life functions as respiration and digestion, even protein folding. In other words, without the constant and changeless operation of the second law of thermodynamics, physical life could not exist.
Ultimately, however, this law leads to dire cosmic consequences. British physicist William Thomson (known as Lord Kelvin) pointed out as early as 1851-52 that the universal dissipation of mechanical energy would inevitable lead to a complete diffusion of heat, the cessation of all motion, the exhaustion of potential energy, and a universal state of death.
This “heat death” follows from the simple fact that the flow of heat from hot bodies to cold eventually brings every bit of matter in the universe to the same temperature. At that point, heat flow everywhere ceases. Everything comes to a complete and final standstill, including consciousness itself. Therefore, if the universe is it, as in the sum total of reality, pessimism and despair represent the only reasonable responses to reality.
On the other hand, if the universe is not the sum total of all that’s real, then our existence may actually hold some meaning. If the “perfect world” people long for exists somewhere beyond this universe, then humanity’s hope, purpose, and destiny may be rooted in reality after all. Of course, the physical laws and dimensions of such a place would need to be different…
Adapted from Why the Universe Is the Way It Is